Adapt Echidna training

[montyly]

We need to adapt the Echidna training to:

• Use https://github.com/crytic/properties/blob/main/contracts/util/PropertiesHelper.sol, and integrate recommendations regarding the properties repo
• Make it compatible with medusa

[gustavo-grieco]

This already started with #361 but needs to be improved to include the DVD examples as well (they are in separated repository)